HELP!!! I've been working on this problem for at least 17 months. Engine quits for no apparent reason. Fineally figured it had to be something in the VATS. It's NOT the key or ignition switch. Found out the KEYPASS module controls the injector drive. When the engine quits the only thing not working is injector pulse. Comes back after a few minutes but drops out again within 3 minutes after re-start. Does anyone know of a way to test this part or bypass it???

 

You say the only thing not working is the injector pulse, does that mean you can crank it over but it wont fire for the three minute waiting period? If so, I doubt it's a VATS problem since it is suppose to not allow you to even turn the motor over.

 

That's correct. It will crank all day but no injector pulse so it won't start. Once it does it will run for 3 to 7 minutes or about 3 miles at best and quit again. After each re-start the next run time is shorter untill it won't start again at all. Have checked and replaced everything else. Even repalced the ECM three times and tried 2 diferent known good PROM chips. According to the manual and schematics the keypass module controls the injector drive. Can't find anywhere how to test or bypass it.

 

Hm, well the modules only costs around $20, so try replacing it. :thumbs:

 

If its the VATS - you'd have nothing, no crank, replace the keyless module...

 

Keep in mind the two signals associated with VATS.

Providing a ground for the start enable circuit is one, the one that shows up first. There is a second signal.

The VATS will reduce a reference voltage thereby telling the ECM the VATS sees the correct resistor. When the ECM sees a volatage drop signal from the VATS, the ECM will pulse the injectors. I believe its looking for around 2.5 volts, down from the 5 volt signal. Am at work and can't give ya the Helm's page number. Gordon K told me there is also a proprietary HZ signal not mentioned in any manual. The two step VATS prevents a "hot wire" start. A thief could jump the wires, get the engine to crank, BUT the ECM will not pulse the injectors. Thus the VATS provides two layers of protection, engine crank and injector pulse.

I doubt signal loss will cause problems after the engine has started and the key moves to the run position. Not sure on this. Suspect the problem is elsewhere.

Interesting problem.

dlmeyers 90 coupe zf6 3 speed shocks

 

kman, if you know where to get one of these for $20.00 please let me know! The Chevy parts man says $435.00, which includes programing to exesting key!!!!

 

dlmeyers, appreciate the info. If you happen to think of what else it could be please let me know.

 

I hate troubleshooting over a keyboard, BUT, give it a try.

If you have the service manual, head for Chart A-3, driveability and emission. A favorite of mine.

Assuming this is an 89 L98, look for "Engine Cranks but will Not Run". The basic idea here is to make sure we know if there is spark or no spark, injector pulse/no pulse, injector voltage but no ground, etc.

So, are you using a "noid" light to determine injector status?. Are you seeing continuous voltage or no voltage on the injector harness. IF the light is illuminated continuously, it does not pulse, the injector driver is not providing a ground. Since you have replaced the ECM, I would suspect the ECM is not seeing an RPM reference signal and then not providing a ground, thus no pulsing injectors.

A little system review may be in order. Anytime the injector harness is powered, harness wires have voltage, the system is just waiting for a ground provided by the ECM's injector driver. The ECM is looking for an RPM signal from the HEI. Your HEI distributor module pin R connecting to Cavity B on the 4 wire connector waaaaay back there on the distributor carries an RPM signal to the ECM(Check your schematics for the 89). I have heard of that connector going bad, the module going bad, etc. IF I were to make a bet, I suspect the ECM is not getting this reference signal and the injector drivers are not providing a ground. Not being able to test this, only going on what is posted. Further, I am very suspicious when "heat" or run time is involved. I lean towards HEI components/RPM reference signal

I am SPECULATING.

Again, head for the service manual trouble shooting steps, do a physical inspection of the distributor wire harness, etc. There is test inolving that connector and cavity B. Keep us informed. Eternally curious.

By the way, I too am starting my New Year out right. Last night, the darn air bag light set a code 16 so I will be wrenching New Years Day. I feel your pain.

Good luck with your repair.

dlmeyers 90 coupe zf6 3 speed shocks

 

dlmeyers, thanks for the input. We suspected that harness early on. I think we discounted it because the tach was still receiving a signal untill the engine stoped turning (after cut out while coasting to a stop). I'm sure it's worth checking into more thoroughly. I will let you know what we find. Thanks again.

 

To bypass a vat system is very simple. take an oem meter and measure the resistance of the little chip on your key, by placing your leads on each side of the chip.Then use a resistor of the same value or within 5% of that value.
Next look under the steering columb area and locate your ign. harness.
You should see what looks to be an orange insolated wire running along with
the ign. harness wires.Cut that in half and inside that are 2 small white wires.
now you have your ign cylinder side and your ecm side.Simply place the resistor across the 2 white wires on the ecm side. and leave the ign side unused. :)

 

The tach signal is different from the RPM signal used by the ECM. The HEI system uses one RPM signal to the ECM and another RPM signal goes through a filter to the dash tach.

Again, good luck.

dlmeyers 90 coupe zf6 3speed shocks